Inaccurate Voltage with IOSD -

Hi friends,
Just added the Mini IOSD device to my Woo Kong Flame wheel Quad - using a Go-Pro and a 5.8Ghz FPV system. I LOVE it so far BUT the on screen voltage is inaccurate. It starts at 12.5 volts (or so) but within a minute of flying it drops to 0.3 volts. The quad flies for several more minutes with no ill results. According to the manual: Real time battery voltage of the aircraft power, unit in V. The value is the same as the protection voltage set in the assistant software. blink: first level low-voltage alert. ​Could this be off since I am not using the voltage protection software? Also does anyone know if they will allow you to change the values from meters to feet and km to mph?
 

R6Media

Member
Hoveringal,
Did you ever get an answer elsewhere? I'm curious about the voltage accuracy as well.
Voltage alarms on my lipo's balance port set to 3.7 and 3.6 just to keep my attention but iOSD is showing me 20volts (3.33 per cell) before I get anywhere close to my 3.6 alarm going off. It's perplexing. I don't know what voltage to believe but iOSD doesn't seem right.
Anyone help?
 

kloner

Aerial DP
al, are you saying it drops to .3v? I'd look at the power connection and where your feeding it from. dry solder joint? Make sure everybody has the current firmwares. there is no way to make the readings not metric that im aware

r6, that is voltage sag. Depending on how hard the packs have been used and there c rating all rigs will see voltage sag. the higher the draw on the packs amp wise, the lower a pack sags. Here is a standard iosd on a jib with 16lbs of payload. it was hovering at 125 amp draw. this was with 20,000mah of 6s


it's a good idea to use a quality charger and never charge faster than the packs recomended rate and to monitor the packs ir through said charger. i charger, hyperion, and fma chargers usually have it.

I don't use the voltage monitoring since it landed me in a river. i let the pack die and get the rig back to safety instead, or at least try. With that feature on it makes it less likely to get to me
 
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R6Media

Member
Kloner,
Thanks! I've never heard of "voltage sag" but I'll be googling it shortly to learn more about it so I understand it.
How did you determine the amperage draw of 125?

The packs I've been flying mostly are Zippys. I bought a variety of C ratings to see if I notice a difference. to date, my 25C-35C 5800mAh pair seems to give me the shortest times but the averages between my 3 pairs is really close. Here's what I have
Zippy Compact 5800 25-35C - 19 flights/cycles, average flight time 8.1 min
Zippy Flightmax 5800 30-40C - 21 flights/cycles, average flight time 7.92 min
Zippy Flightmax 5000 45-55C - 16 flights/cycles, average flight time 8.6 min

I never fly my s800 hard and i charge and balance at 1C with Hyperion EOS07201Net3AD's

Anyway, that was a lot of info you probably don't care about but let me ask... are you suggesting that the voltage shown is the accurate voltage under load?
I have my voltage protection set at 19.2 as my red-alert final warning but I'll never fly it to that (3.2v) I'm always landing once I see it sticking at around 20.0 but I'm totally fearful of it hitting its 19.2 behind the scenes without really showing me that voltage since the difference doesnt seem very big between 3.33V and 3.2V. I've been debating turning it off since I feel like I'm monitoring enough but now I feel like the balance port voltage alarms are absolutely useless if the iOSD is the accurate number. Why do you think the voltage alarms don't pick up the current "under load" voltage?

I also noticed in your video that you changed packs when you were landing at 21.3V. Is that your personal cutoff? I read some other post suggesting never to fly your packs below 3.5-3.7 under load. Jeesh if I did that, I'd get 4 minute flights!

Thanks.

One more thought.... what do you think is more important for a happy healthy lipo and a crash free existance due to power loss: the final resting voltage that shows you've used 75-80% of its capacity (based on the 80% rule) or the under load voltage and trying to keep THAT NUMBER with 20-25% to spare? knowing that when you land and shutdown you'll probably have maybe 40% left. Just curious.
 
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kloner

Aerial DP
it was landing at 21.3 but the rest voltage was 22.5 still...... that is the sag. That was an exceptionaly heavy load, 16 lbs on the hanger. with a dslr the thing barely sags, but it hovers more like 40-50 amps in that state

I have an engineer for a camera man so we flew the rig a minute, recharged the packs and noted the amp draw. if he saw this post he'd tell you your amp draws based on your flight times above

were on gens ace
 

R6Media

Member
Thanks Kloner. I have a pair of nano techs and a pair of Thunder Powers to solder up and try still. I wonder how they will perform.
It sounds like it's good to have an engineer.
Def more testing for me in the near future.
 
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kloner

Aerial DP
usually nano show a ton of sag, thunder power usually have a super low internal resistance and sag should be minimal.

When these cells hit 80%, they start getting lazy and you can feel it. at least i can, it stops reacting right and voltage goes from dripping off .1 volt at a time to multiple volts at a time in the matter of 30 seconds, less if a really big draw
 

R6Media

Member
"thunder power usually have a super low internal resistance and sag should be minimal"

hence the price tag :). I'm looking forward to seeing what they can do.
 

kloner

Aerial DP
log all the internal resistance and keep track of what is doing what. That's the best way to "watch" a pack, i mark it on the sides of each pack and look at it every other gig. usually just look at the main connector and only dig deeper if it has changed. as in look at each cell. pretty sure that charger you mentioned has it.

Internal resistance
 

R6Media

Member
i do. i don't log it but i check regularly. all my packs have an IR under 3 at the moment. usually 2.2-2.8
good idea to simply add a column to my flight log spreadsheet. thx
 

R6Media

Member
Kloner or anybody.... does this seem indicative of the "voltage sag" you mentioned earlier? I really want to understand this.
It makes no sense to me why the iOSD reads different. Get that engineer camera operator of yours over here. :)
 
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kloner

Aerial DP
is there a weird wiring setup powering the osd or is the power cables on it nice and soldered in to a big power source? It creeps in voltage like it's real but the other gauge not showing it is odd. I've never really looked at it like this with 2 methods simultaneously but i carry some big loads with some big packs and never seen it as drastic of sag as you do there.

we decided you checked the ir of the pack and its good?
 

Tahoe Ed

Active Member
What controller are you using? Which version of the iOSD including the firmware are you using? Not an interrogation just want to understand what you are going through.
 

R6Media

Member
Sorry for the delay guys...holiday.
Tahoe Ed: I'm flying Wookong with iOSD Mark II firmware version 2.0
Kloner: Yeah no weird setup. Standard DJI connection stuff, and I just checked IR of all my packs. Every cell in every pack is between 1.5-2.3
 

R6Media

Member
So last night I performed the test again and checked out the data in the iOSD DAT file. I'm not gonna lie, I don't know how to read everything in the DJI Data Viewer (thanks DJI for leaving yet something else completely cryptic) but the "Main Voltage" under FLY DATA seemed like common sense to look at.

Test was done on my Zippy 5000mAh 45C dual packs. IR of all cells between 1.5-2.2
Total length of the flight was 7 minutes in a simple 6 foot hover.
I took readings every minute comparing iOSD feedback to the Wattmeter directly connected to the power source:

Startup: 25V
1 minute: iOSD: 21.1V WattMeter: 22.7V Difference 1.6V
2 minute: iOSD: 20.6V WattMeter: 22.4V Difference 1.8V
3 minute: iOSD: 20.1V WattMeter: 22.0V Difference 1.9V
4 minute: iOSD: 19.9V WattMeter: 21.8V Difference 1.9V
5 minute: iOSD: 19.8V WattMeter: 21.6V Difference 1.8V
6 minute: iOSD: 19.7V WattMeter: 21.4V Difference 1.7V

Here's a screen cap of the data log Main Voltage pulled from iOSD after flight:

View attachment 14935

The only thing I can think of is since the power is routed through so many things before it gets registered in the iOSD, would that explain such a huge difference? I don't see how that would matter.

-The Wattmeter is directly connected between the batteries and the s800 main power connection.

-The Wookong PMU is connected the the PMU XT60 connector via the top plate. Due to its positioning in front of the main power connector I assume its sharing circuitry. Because the PMU has limited CAN BUS connections, the GPS Antenna Module connects to the side and routes to aircraft top plate. The GPS antenna Module itself has a CANBUS port on it. That is where my iOSD is connected to derive it's power source. There is no other option.

If you'd like to see the DAT file itself, let me know since I can't upload it here.

Thanks.
 

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kloner

Aerial DP
is that fma charger number?

try checking the ir of just the main pack connector..... the individual cells shows what the cells are, the one connector number shows you the loss in the connector.... what connector are you using to the main packs?

those voltages look pretty close to normal. might be a half a volt lower than i'd expect. i was flying towards the end of a pack the other day, 800 with twice the wattage of a s800 and it was sagging down to 20.2 and landed at 22.1. the graph is how these usually look..... flatter the better but it has to drop voltage somehow.

the osd has it's own power plug, it shouldn't be powering through the can..... big thick red and black wires.... if your saying there not hooked up,,,, there ya go.
 


R6Media

Member
Kloner/Tahoe Ed - sorry my mistake on the iOSD getting it's power from the CAN BUS. my setup is very neat and I can't see all the connections in there. I made the assumption based on what I saw. Watching the iOSD install video i remember now that it has XT60 connector. Upon closer inspection... my iOSD XT60 power pigtail is shared with the power connector for the PMU connection and not the Main Battery connection. I don't see this as a problem do you? I assumed the thick wires (main battery connection) was just direct to battery with nothing in between.

View attachment 14958 View attachment 14959

Kloner: I don't know what you mean by FMA Charger Number, sorry. My packs and connectors for main power are all EC5's. I'm assuming you mean for me to check the IR of the connectors with a multimeter?
 

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